there probably is more to the story, however just having keys in the ignition is not an offence. having the engine running is ! it would also apply to any hand held device apart from a 2 way radio.
so i would hazard a guess that if there was nothing else in play that warranted the interaction then that rider had his bike running even though he had his helmet off.
https://www.askthe.police.uk/faq/?id=ac2e6341-7ac9-ed11-b595-0022483eff86
"Mobile phone - use when parked
Whether someone is driving in terms of the law is a question of fact and degree and is ultimately a matter for a court to decide.
If you are sat in the driving seat of a vehicle on a road with the engine running you will usually be deemed to be driving for the purposes of this offence. There have even been cases where people have been found to be driving when they have let the vehicle roll forward without the engine running. In order to ensure you don't break the law in relation to using a phone/device when parked in a safe and lawful place, we would suggest the following:
- Use a hands-free kit
- Use the phone/device outside the vehicle
- Ideally, don't use the phone/device at all"
